Motor vehicles, as presently manufactured, are equipped with systems for defogging and deicing windshields. Generally these systems depend upon heat generated in the internal combustion engine and transferred to the engine's cooling system to be blown as warm air across the interior of the windshield to accomplish the defogging and deicing. In such a case, of course, it is readily apparent that there is a period of time between the starting of an engine and the time that sufficient heat is being generated in its cooling system in order to provide a defogging and deicing of the vehicle's windshield. Depending upon the exact temperature conditions and the time the vehicle has been sitting idle without its engine running, the period of time before sufficient heat is available to accomplish this function can be up to 10 minutes or more.
In view of the fact that there can be a rather lengthy delay before the present day motor vehicle's heating and defrosting system can clear a windshield, automotive designers have been attempting to design systems which generate heat from electrical energy to accomplish a relatively rapid defrost and deicing of a vehicle windshield. Such an electrically heated defrosting and deicing system generally would be independent of the normal heating and defrosting system contained in a motor vehicle.
Many different systems have been proposed for accomplishing this rapid defrost and deicing function, including the placement of an electrically conductive transparent coating on the windshield and embedding fine wires in a laminating interlayer of the windshield. To the best of my knowledge there are no such rapid defrost and deicing systems in vehicles which are currently sold in the U.S. market. I believe this is because of the relatively high cost of such systems and also because of the electrical problems associated with the installment of such a system on a vehicle windshield such as found in today's automobiles. The windshield found in today's automobiles is generally of trapezoid shape. By this I mean the modern day windshield is smaller in length dimension at the top thereof than at the bottom thereof. The top dimension of the windshield is reduced because the aerodynamic styling of motor vehicles dictates such a configuration for the windshield to fit on the rounded body shapes now being manufactured.
I personally conducted a search in the U.S. Patent and Trademark Office to determine if the electrically heated windshield construction of my invention was novel. During this search, I uncovered many patents dealing with heated window constructions. However, of the many patents that I did look at, I believed that none really were relevant to the electrically heated windshield construction of my invention. However, I would like to point out the teachings of four U.S. patents that were of some interest to me simply for their showing of a development of electrically heated window structures.
U.S. Pat. No. 957,728 issued on May 10, 1910 for a "Window." This patent shows a window for vehicles which includes a pane of glass, conducting wires embedded in the glass, and a device for automatically throwing the wires in circuit upon closing of the window and opening the circuit upon opening of the window.
U.S. Pat. No. 3,313,920 issued on Apr. 11, 1967 for a "Heater Panel." The heater panel shown comprises at least one electrically insulated glass sheet with an electrically conductive transparent film formed thereon. A single pair of electrodes extended parallel to each other in contact with the conductive transparent film. The film had a plurality of grooves extending between the electrodes for isolating the film on either side of the grooves to define a plurality of isolated strips of conductive film extending from one electrode to the other and in electrical contact with such electrodes.
U.S. Pat. No. 3,947,618 issued on Mar. 30, 1976 for an "Electrically Heated Transparent Panel." The electrically heated transparent panel described in this patent is a laminated safety glass windshield construction. This construction has a clear polymer interlayer with a pattern of wrinkled resistance wires oriented in a three dimensional nonparallel random fashion so as to reduce glare from wires when the window is used in an automotive or other type of vehicle. It is quite obvious that this construction did not find wide acceptance as I am unaware of any commercial development of this style of electrically heated window.
U.S. Pat. No. 4,361,751 issued on Nov. 30, 1982 for "Electroconductive Window Having Improved Bus Bar." This patent discloses an electroconductive laminated window having an electroconductive coating applied to one interior substrate surface with a pair of bus bars electrically connecting a source of electrical potential thereto. The bus bars include an electroconductive layer having volume resistivity less than about 10.sup.-2 ohm/cm interposed between and conformable to the surface configurations of the electroconductive coating and a flexible metallic current carrying member. The metallic current carrying member is preferably a mesh of thin copper foil which is substantially bendable in its own plane. The electroconductive layer is preferably a metallic layer substantially free of nonmetallilc components consisting of a mixture of finely divided electroconductive particles and finely divided metal alloy particles having a fusion temperature between about 70.degree. C. and about 150.degree. C.
The structures discussed above are substantially different than the electrically heated windshield which includes the improved bus bar configuration of my invention. The improved bus bar configuration of my invention finds particular use in an electrically heated windshield construction which is used as the forward vision unit of a motor vehicle such as an automobile or a truck.